Rare earth magnets (especially permanent magnets) represented by Nd—Fe—B-based magnets exhibit considerably high magnetic characteristics. The use of such rare earth magnets allows electromagnetic devices and electric motors to be reduced in size, enhanced in output power, and implemented with high density, and also enables reduction of environmental burdens etc, so the application of rare earth magnets is being investigated in various fields.
In order to achieve the above, however, it is required for rare earth magnets to stably exhibit such excellent magnetic characteristics for a long period of time even under severe environments. To this end, research and development are actively conducted to enhance the coercivity effective to heat resistance property (resistance for demagnetization) and the like while maintaining or further improving the high residual magnetic flux density of rare earth magnets. One of the most effective methods therefor is to cause diffusion elements, such as dysprosium (Dy) and terbium (Tb), which are rare earth elements having large anisotropy magnetic fields (Ha), to be diffused to grain boundaries and the like of crystals as main phases (e.g. Nd2Fe14B-type crystals). This allows the improvement of magnetocrystalline anisotropy and the suppression of nucleation of reverse magnetic domains while suppressing the substitution of Dy and the like in those crystal grains, and also allows the improvement of coercivity while suppressing the deterioration of residual magnetic flux density.
Meanwhile, there are various methods for such diffusion. For example, powder mixing method is known in which diffusion powder that includes diffusion elements is mixed with magnet powder comprising raw material alloy (rare earth magnet alloy) and the obtained powder mixture is formed into a compact such as to be sintered thereby performing the above diffusion treatment. In addition, adhesion method is also known in which diffusion powder or the like is caused to adhere to the surface of a magnet material and heat treatment is then performed for diffusion treatment. Furthermore, vapor deposition method (vaporization method) is proposed in which, to effectively improve the coercivity while suppressing the amount of Dy and the like as rare elements to be used, diffusion elements are vapor deposited on a magnet material comprising magnet powder thereby to be diffused inwardly. This vapor deposition method is the recent mainstream, details of which are described in the patent literature below, for example.